Stepped-frequency range profiling of multiple overlapped targets

It is a challenging task all along for modern radar systems to detect and recognize multiple targets in heavy clutter. Stepped-frequency radar (SFR) can acquire high range resolution profiles (HRRP) to improve the performance of target recognition greatly. Moreover, SFR can suppress clutter by increasing the pulse repetition frequency (PRF) as well as decreasing the product of the pulse width and the frequency step. However, as PRF increases, range measurement becomes ambiguous, so multiple targets in the same formation will probably overlap each other along the range axis. Accordingly, this paper puts emphasis on solving this overlap problem, namely, estimating HRRP of each overlapped target. It firstly analyzes the special characteristics of the SFR echoes received under the condition of range ambiguity. Then, considering envelop-weighting modification and non-modification to each HRR cell, it proposes two estimation methods, the first of which is based on maximum likelihood estimation (MLE) and reaches the Cramer-Rao low bound (CRLB). Monte Carlo simulation results have verified the validity of the theoretical analysis.